I want potential benefits to be so small such that no player of a fighter feels compelled to carry around more than three or four weapons

Instead of starting with a list of weapons, perhaps it would be better to start at the end and ask: How many weapons should the list have? How many features will I therefore need to differentiate between them all?

Polearms are good for unhorsing knights using the hook, cutting down people using the axe blade, and hammering knights in armor, but bad in close combat

Knives and short swords are good in close combat

Flanking ignores shields

Charging and setting weapons against a charge inflicts more damage; the longer weapon strikes first

It’s easier to aim a crossbow at something compared with a longbow.

The longbow’s range is higher.

Shortbows can be used on a horse.

Bows and crossbows are armor-piercing.

Things I’ll ignore:

Halberds can be used to trip, but I hate tripping and other combat maneuvers. I’ll just ignore that and treat halberds like polearms.

Heavy two handed weapons inflict lots of damage against unarmed opponents, and I don’t want to make them slower. Not being able to use a shield is punishment enough. This also takes care of the overrated two-handed sword.

And then I suddenly go whaaaaaaa… This is too damn complicated. It’ll result in a minigame where people start optimizing weapons against armor, it’ll introduce discussions of what was developed in reaction what, the exact time period equivalent we’re playing in, and I don’t want to go there.

But I cannot resist… How about this? The effective bonus would mean “ignores part of the protective value of the armor”. The “Chains” column is for all sorts of flails. We’re ignoring tripping, disarming, and all sorts of other combat maneuvers. Those should be resolved by common sense instead of rules.

Weapon vs. Armor Type

Slashing

Piercing

Bludgeoning

Chains

Unarmed (AC 9)

0

0

0

0

Leather (AC 7)

+1

0

0

0

Chain (AC 5)

0

+1

0

0

Plate (AC 3)

0

0

+1

0

Shield (AC -1)

0

0

0

+1

What about Monsters, you say? Easy. Anything wearing armor is resolved as indicated above. Most things having a “natural” armor shall be considered wearing leather armor. This makes swords a good choice against all sorts of monsters, which is a nice touch.

What remains to be handled:

Two handed or two weapon fighting deals more damage but prevents the use of a shield.

Shields may be splintered.

Some weapons can be used for a charge (lance), or set against a charge (longspears). In this case attacks are not resolved according to initiative but before all others according to weapon length.

Another cool idea is to let the weapon specify initiative. I feel daggers should be faster, and that torches doing 1d6+1d4 damage makes them the most terrifying weapon, etc. But I like the idea. Playing with Initiative.

Speaking of initiative, check out my continuous initiative house rules which are based around the idea that in the same time frame as one mighty swing of a two handed sword, a skilled knifesman can jab a number of times.